Once you sketch a line, the Insert
Line PropertyManager changes to the Line
Properties PropertyManager, and you can continue sketching 3D lines.
To change Options, click OK 
to return to the
Insert Line PropertyManager.Enables you to sketch multiple 3D lines.
Only As sketched is available with 3D sketches.
With the click-drag method, sketch a line in any direction until you release the pointer.
With the click-click method, sketch a line in any direction, and continue sketching other lines in any direction, until you double-click.
Select either or both options:
For construction. Creates a construction line.
Infinite length. Creates a line of infinite length that you can later trim.
Once you sketch a line, the Insert
Line PropertyManager changes to the Line
Properties PropertyManager, and you can continue sketching 3D lines.
To change Options, click OK to return to the
Insert Line PropertyManager.